Artificial and Natural Hybrids in the Gramineae, Tribe Hordeae. VII. Hybrids and Allopolyploids between Elymus Glaucus and Sitanion Spp.

N the first paper of this series (STEBBINS, VALENCIA and VALENCIA I 1946a) two different natural hybrids between Elymus glaucus and Sitanion jubatum were described. Both were intermediate between their parents and were completely sterile. They nevertheless had essentially normal meiosis, with the chromosomes forming 14 bivalents or occasionally 13 bivalents and 2 univalents at first metaphase. During the past seven years a series of artificial hybrids has been made between various strains of E. glaucus and S. jubatum as well as the closely related S. hystrix. Because of the relative vigor of E . glaucus and the extreme drought resistance of many strains of Sitanion, the senior author has hoped that progeny from such hybrids would yield vigorous, drought-resistant grasses for revegetating the dry range lands of California. For this purpose, most of the hybrids have been treated with colchicine in order to produce allopolyploids from them. The results of these experiments have revealed a remarkable array of different types of behavior after hybridization between different strains supposedly belonging to the same taxonomic species. In some instances the F1 hybrids were easily obtained, vigorous, and yielded allopolyploids which were highly fertile in the doubled sectors of F1 plants and gave second generation progeny (C,) containing many vigorous, fertile plants. At the other extreme are examples of hybridizations which failed even after repeated attempts and of FI plants which were so weak that they did not flower. The present contribution presents these results, along with preliminary considerations regarding their interpretation. The cytological studies of the allopolyploids were made by the junior author during the year 1951-1952. The initial hybridizations and the morphological studies of the hybrids were made by the senior author and his assistants.